The present invention relates to a method of manufacturing a sensor having a magnetic film, and more particularly, a sensor having a magnetic film which measures a torque received by a shaft member, and rotating speed and rotating angle of the shaft member accurately.
There has been a known method of manufacturing a sensor having a magnetic film by spraying a molten magnetic material to form a magnetic film on the surface of a shaft member, and a known method of measuring a torque received by the shaft member by utilizing the characteristic of the magnetic film of the sensor (The Japanese Patent Application Laying Open Gazette No. 61-53504).
When particles consisting of crystals are used for a magnetic material and a magnetic field is impressed upon the particles, the domain walls of the particles move so that each volume of the domains spontaneously magnetized in the direction of the magnetic field is increased and also the magnetization along with the magnetic field is increased.
In this case, the smaller the particles used for magnetic material are, the more the number of domain walls of the magnetic film becomes, so that a strong magnetic field can be impressed upon a magnetic film, and a number of domain walls move. Consequently, even after the value of the magnetic field impressed upon the magnetic film has returned to 0, regenerated output at the time of measuring is increased, as well as a reverse magnetic field necessary to make the value of coercive force, that is, a residual magnetization 0 is increased because high residual magnetization can be obtained by a number of domain walls which has once moved.
However, in the case of thermal spraying of the above mentioned minute particles by plasma spraying on a member to form a magnetic film on the surface of the member, the thermal spraying particles are so light that they cannot be supplied to the flame of the plasma spraying or they are struck and scattered by the flame. Namely, there is raised a problem such that the thermal spraying particles are not accurately adhered on the member to be sprayed.
Accordingly, the number of the above mentioned domain walls cannot be increased beyond a certain extent because minute particles consisting of crystals cannot be used as thermal spraying particles. Therefore, according to a conventional method, there is a problem such that a magnetic film of high regenerated output and of high coercive force cannot be formed on a member to be sprayed.